Implement availability triggers for lights and blinds actuators in AI-MAS lab

### Why
Context information from web-enabled devices should be advertised _only when_ these devices are actually available (e.g. plugged in).
To maintain consistency of implementation for the AI-MAS lab devices, triggers of availability should be based on notifications sent over the ROS-based AMIRO framework.

### What
- [x] Implement ROS service to query for the availability of Philips Hue lights
- [x] Implement ROS channel to signal notification of light being available or not
- [x] Implement ROS service to query for the availability of blinds
- [x] Implement ROS channel to signal notification of blinds being available or not

### Notes